A polycarbonate resin has been used as a material for molded articles in various industrial fields because the resin is excellent in mechanical properties, thermal properties, and electrical properties. In recent years, in association with expansion of application fields, performance required for the polycarbonate resin has also become diversified. It may be unable to sufficiently meet such requirement by only using a conventional polycarbonate resin, for example, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) or 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z) as a raw material. Therefore, in order to meet such requirement, polycarbonate resins having various chemical structures have been proposed depending on the applications and required characteristics.
An example of such functional products is an electrophotographic photosensitive body using a polycarbonate resin as a binder resin for a functional material such as a charge generation material or a charge transport material.
The electrophotographic photosensitive body is required to have predetermined sensitivity, predetermined electrical characteristics, or predetermined optical characteristics in accordance with an electrophotographic process to which the electrophotographic photosensitive body is applied. Operations such as corona charging, toner development, transfer onto paper, and cleaning treatment are repeatedly conducted on a surface of a photosensitive layer of the electrophotographic photosensitive body, and hence electrical and mechanical external forces are applied to the surface every time these operations are conducted. Therefore, the photosensitive layer provided for the surface of the electrophotographic photosensitive body is required to have durability against those external forces in order that quality of electrophotographic images may be maintained over a long time period. In addition, the electrophotographic photosensitive body is ordinarily produced by a method involving dissolving a binder resin in an organic solvent together with a functional material and casting the solution on a conductive substrate or the like to form a film. Accordingly, solubility in, and stability against, the organic solvent are required.
The polycarbonate resin using, for example, bisphenol A or bisphenol Z as a raw material has not been sufficiently satisfactory in terms of durability when used as a binder resin for an electrophotographic photosensitive body. In view of the foregoing, various approaches have been adopted to meet such requirement. A polycarbonate copolymer is known as an effective technology for improving wear resistance of a photosensitive layer.
As an example, Patent Document 1 discloses a polycarbonate copolymer having a bisphenol Z skeleton and a biphenyl skeleton as a binder resin excellent in abrasion resistance. However, an additional improvement in abrasion resistance has been required in association with an improvement in performance of a copying machine in recent years.
Accordingly, a polycarbonate copolymer obtained by using a raw material in which a repeating number of monomer unit in the polycarbonate oligomer is reduced and improving a copolymerization ratio of a skeleton contributing to abrasion resistance has been developed and disclosed in Patent Document 2.
Meanwhile, Patent Document 3 discloses a urethane bond-containing polycarbonate composed of a polycarbonate oligomer and an aromatic diamine as a technology for improving electrical characteristics of an electrophotographic photosensitive body with a structure except a polycarbonate copolymer.
In addition, Patent Document 4 discloses a polyester polycarbonate having: a polycarbonate unit derived from a dihydric phenol having a specific structure; and a polyester unit derived from a dicarboxylic acid having a specific structure.
However, each of the polycarbonates disclosed in those documents has insufficient abrasion resistance, or has a problem in terms of, for example, electrical characteristics or stability of a coating liquid.